I'm a climate scientist. I got to meet Will.i.am on Monday (apologies for the name-drop, but my daughter assures me that he is definitely the safest person a university professor is every likely to meet). He arrived in a helicopter. Lots of sanctimonious journalists then got upset about his carbon footprint.

Which gives me an opportunity to explain why nagging people about their carbon footprint, or worrying about your own, is essentially irrelevant to the issue of climate change. Worse, guilt-tripping individuals provides a handy distraction from our failure to make any progress at all on the measures actually necessary to solve the problem.

Carbon emissions from fossil fuel use and deforestation are currently approaching 300 tonnes per second: check trillionthtonne.org to see what this means. And once it is out there, it accumulates. So the brutal truth is that just burning carbon slower doesn't help: Will.i.am forgoing his helicopter for the train via Reading would have saved the world from global warming for less than a millisecond.

Even if you were, heroically, to reduce your personal carbon footprint to zero for the rest of your lifetime, you would only buy the rest of us a second or two before accumulated carbon emissions were exactly back to where they would have been without your efforts.

"Yes, but if we all were to join in …" the environmentalists reply, betraying a fundamental disconnect with the way free markets work. When a resource is as useful as fossil energy, individual abstinence is not a way to reduce overall consumption. Even if Europe as a whole were ever actually to reduce consumption with a cap-and-trade scheme, reduced demand would depress fossil fuel prices, and consumption would bounce up elsewhere.

"So we need a global cap-and-trade regime …" – but beware what you wish for. Because carbon accumulates in the atmosphere, we aren't going to stop global warming until the net flow of fossil carbon out of the ground is virtually zero. Claiming you can do this with a global emission cap means you believe that someone, someday in the not-too-distant future, will have the power to regulate and ultimately ban every human activity that involves the burning of fossil fuels.

"So are we doomed to let the world warm?" On the contrary, the solution is perfectly simple. Anyone who extracts fossil carbon out of the ground should be obliged to put a fraction of that carbon back underground in the form of "sequestered" (buried) CO2. If the sequestered fraction is tied to the accumulation of carbon in the atmosphere, we can ensure that it converges on 100% before we release too much, and everyone can carry on using fossil carbon to their hearts' content for as long as they can afford to do so.

This will, of course, make fossil fuels somewhat more expensive for consumers: but the fuel tax you pay far exceeds the cost of burying enough carbon to compensate for the climate impact of your driving. So don't let any politician kid you that those taxes are preventing climate change.

I suspect Will.i.am could still afford his helicopter, and why not? He writes songs people want to listen to. It's odd that newspapers that are normally champions of the free market get upset about Will.i.am's carbon footprint: I don't hear any of them complaining about the size of his financial footprint.

At present, our approach to promoting carbon sequestration is to subsidise the building of pilot plants, which are then cancelled whenever the public finances get tight. Why waste taxpayers' money? The fossil fuel extraction industry will ultimately need sequestration to neutralise the impact of their products on the climate, so they should simply be instructed to get on with it as a condition of remaining in a highly profitable business.

At Oxford, we suggested the idea of Safe carbon (Safe stands for sequestered adequate fraction of extracted carbon) in December 2009. At the time, everyone told us to shut up because it might distract attention from the UN climate process. But with that process looking more moribund by the year, surely it is time for some different ideas?